1. Field of the Invention
This invention relates to an apparatus for operating a double-acting fluid or electrically powered actuator, and more particularly to a manual control for mechanically extending or retracting an actuator rod in the event of a failure of the primary fluid or electrical means of controlling the actuator.
2. Description of the Prior Art
Double-acting actuators, either hydraulically or electrically powered, are commonly used to open and close various types of valves employed in the testing, production and shutting down of oil and gas wells in the petroleum industry. In such use the actuator is mounted on the well Christmas tree, and the actuator rod is connected to the valve closure element so that axial movement of the rod between its extended and retracted positions results in opening or closing the valve. The hydraulic or electrical power source is usually at a remote location from the well, especially in the case of offshore or subsea wells, and is connected to the actuator by hydraulic or electrical lines that may extend for a considerable distance. If any of these lines are damaged, or if they sufficiently deteriorate, the actuator very likely will malfunction, resulting in a loss of control of the associated valve which thereby could be locked into an open position, thus allowing petroleum products to escape, or in a closed position which would prevent testing the well and/or production of petroleum therefrom.
Prior art override controls for such actuators include apparatus which can be bolted or clamped to the actuator rod when there is a failure in the primary control system, to move the actuator rod, and thus the associated valve, into the desired position. When the primary control system is repaired, the prior art override apparatus must be removed before the actuator can be used in the normal manner. What is needed is an override control that can be installed in working position on the actuator, meanwhile allowing the actuator to be hydraulically or electrically controlled until a failure occurs, at which time the override control can then be used until repairs are completed and normal control is resumed.